In "The Idea of the Holy," Otto embarks on a profound exploration of the psychological and phenomenological dimensions of numinous experiences while offering an apologetic rationale for Christian faith through a subjectivist lens. Engaging with the tradition of German idealism, he navigates the duality between the spiritual and material realms. Otto stresses that perceptions of the holy are a priori cognitions, independent of empirical experiences. This spiritual realm, in his view, encompasses emotional experiences that find justification not through empirical evidence, but through nonrational beliefs and intuitions.

Otto posits that although the capacity to perceive the holy is not innate, it is a potential within every individual, capable of cultivation to varying extents. Certain figures, notably the Hebrew prophets and Jesus, exemplify a heightened receptivity to numinous revelations, illustrating how deeply embedded spiritual experiences can manifest within individuals.

Central to Otto's argument is the concept of divination, a psychological faculty he describes as essential for recognizing manifestations of the holy. Drawing inspiration from Friedrich Schleiermacher’s theories, which prioritize “intuitions and feelings” in religious faith, Otto proposes that divination facilitates contact with a spiritual reality that transcends individual existence. He likens this faculty to aesthetic judgment, perceiving it as informed by a "predisposing inner witness of the Spirit." Otto concedes, however, that his defense of intuitive religious experiences may resonate only with those predisposed to accept religious consciousness as a given.

Otto extends a respectful nod to various religious traditions yet contends that the Christian religious experience has engendered a uniquely profound and vibrant religious intuition. His focus, however, shifts from scrutinizing the veracity of cognitive beliefs to emphasizing the moral dimensions encapsulated in the life and teachings of Jesus. To Otto, the miracles attributed to Jesus serve less as historical claims and more as metaphorical symbols embodying his "exalted spiritual powers over nature." This perspective suggests a degree of skepticism towards the literal interpretation of traditional Christian doctrines such as the atonement, the Trinity, and personal consciousness in an afterlife, indicating a nuanced approach to these dogmas.